Cost to Build a Bathroom in a Home Extension or Granny Flat in Melbourne (2025 Guide)
Building a new bathroom for your home extension or granny flat in Melbourne isn’t as simple or cheap as most homeowners expect. In 2025, the cost can range anywhere from $25,000 to over $60,000, depending on design, materials, and compliance requirements. This guide breaks down what drives those costs, where people go wrong, and how to build smarter without overspending.
Fast Facts
- Average Cost: Building a new bathroom in a Melbourne extension or granny flat ranges from $25,000–$60,000.
- Timeline: Expect 6–12 weeks for design and permits, plus 4–8 weeks for construction.
- Permits: Building permit required; planning permit not needed for small second dwellings under 60 m².
- Hidden Costs: Waterproofing, site access, and plumbing can add 15–20% to your budget.
- ROI: A well-built bathroom can add up to 10% to your property’s value.
The Unexpected Price Reality Behind Melbourne’s Extra Bathroom Dream
It often starts with a simple plan: adding an ensuite to make life easier or a granny flat to bring in extra income. Many Melbourne homeowners think a small bathroom will cost around $20,000, but actual quotes usually land closer to $45,000–$55,000 once plumbing, waterproofing, and permits come into play.
Bathrooms are the most expensive rooms per square metre to build because they require precision and multiple trades such as plumbers, electricians, tilers, and waterproofers, all working in a confined space. That’s why understanding the real cost early is critical before any walls go up.
How Much Does a Granny Flat Bathroom Cost in Melbourne?
Adding a new bathroom in an extension or granny flat is different from renovating an old one. You’re not just replacing tiles; you’re building everything from scratch, including plumbing stacks, waterproof membranes, drainage, and fixtures that meet Victorian Building Authority (VBA) standards.
2025 Cost Ranges in Melbourne
| Build Type | Size | Estimated Cost | Typical Features |
|---|---|---|---|
| Basic | 4–6 m² | $25,000–$35,000 | Standard shower, toilet, basic vanity, simple tiles |
| Mid-Range | 6–8 m² | $35,000–$50,000 | Freestanding bath, premium fittings, feature tiles |
| Luxury | 8–10 m²+ | $50,000–$80,000+ | Heated floors, smart toilet, skylight, double vanity |
In a 50 m² granny flat, which typically costs $130,000–$190,000 in total, the bathroom and kitchen together often consume $15,000–$25,000 of that budget. The bathroom alone can easily account for $10,000–$15,000, depending on finishes.
Where the Money Goes
Typical mid-range $40,000 build:
- Labour: $22,000 (55%)
- Materials: $14,000 (35%)
- Design, Permits, Contingency: $4,000 (10%)
Average Labour Rates (Melbourne 2025):
- Plumber: $100–$150 per hour
- Electrician: $80–$120 per hour
- Tiler: $50–$130 per m²
Why Extensions Cost More Than Simple Renovations
Renovations upgrade what’s already there. Extensions and granny flats, on the other hand, mean starting from the ground up.
Main reasons costs rise:
- New plumbing and drainage: connecting to the main sewer is complex and expensive.
- Structural work: new walls, roofing, and insulation add 10–20% more.
- Site access: tight driveways or live-in homes make trade coordination harder.
- Compliance: new builds must meet updated waterproofing and energy efficiency standards.
Even minor design errors, like a poorly planned drain slope, can cost thousands to fix later. For this reason, experts suggest budgeting an additional 15–20% contingency to cover unexpected issues.
Hidden Costs and Traps to Watch Out For
Bathroom builds are notorious for hidden costs. Here are Melbourne’s biggest money traps:
- Waterproofing mistakes: a failed membrane can cause $5,000–$15,000 in repairs.
- Permit delays: building permits can take 4–8 weeks.
- Old house issues: asbestos, narrow access, or heritage overlays can add 10–20% extra.
- Material price increases: tiles, fittings, and labour have risen up to 15% in 2025.
- Unregistered trades: fixing poor workmanship later doubles your cost.
CHOICE lists waterproofing as one of the most common bathroom defects in Australia. That’s why engaging registered trades with VBA credentials is essential.
Related Insight
If you’re comparing renovation options, discover whether a bathtub replacement or a full remodel fits your Melbourne home and budget better.
Permissions, Trades, and Timeline for Melbourne Builds
Key Rules for Victoria (2025 Updates)
- Small second dwellings (granny flats) under 60 m² don’t require a planning permit, but a building permit is mandatory.
- Projects over $16,000 must use a VBA-registered builder with Domestic Building Insurance.
- If the site is occupied, work must follow strict safety and staging requirements.
Typical Trades and Costs
| Trade | Task | Estimated Cost |
|---|---|---|
| Builder / Project Manager | Overall coordination | $5,000–$10,000 |
| Plumber | Stack and drainage setup | $8,000–$15,000 |
| Electrician | Power, lighting, exhaust | $2,000–$5,000 |
| Tiler & Waterproofer | Walls, floors, sealing | $5,000–$10,000 |
Timeline
- Design and Permits: 6–12 weeks
- Build and Fit-out: 4–8 weeks
- Occupied site: add about 2 more weeks
Tip: Get fixed-price quotes and check licences on the Victorian Building Authority website.
Smart Design Choices for Value and Longevity
A beautiful bathroom doesn’t need to be expensive. Smart planning and practical material selection often bring better long-term results.
Recommended value choices:
- Tiles: porcelain over marble; $30–$55 per m² for durability.
- Fixtures: quality mid-range fittings instead of premium designer brands.
- Layout: compact designs save space and labour.
- Ventilation: mechanical exhaust fans prevent moisture damage.
Trending 2025 styles: walk-in wet rooms, storage niches, LED mirrors, and matte-black tapware. However, in granny flats, avoid high-maintenance materials and focus on function, not flash.
ROI: A well-built bathroom can return 60–70% of its cost at resale and boost property value by up to 10%. For rental units, new bathrooms often improve yield by 10–12% annually.
Melbourne Homeowner Checklist: Build Smart, Avoid Regrets
- Budget: Expect $30,000–$50,000 mid-range plus 20% contingency.
- Ask builders: Are you VBA registered? Is Domestic Building Insurance included?
- Get at least three quotes: Compare scope and inclusions carefully.
- Confirm permits: Building permit always; zoning check with local council.
- Avoid shortcuts: DIY plumbing is illegal and unsafe.
- Protect waterproofing: Use certified installers and request a warranty certificate.
- Plan logistics: If living on-site, set up temporary facilities in advance.
These steps can easily save $10,000 or more by preventing rework and fines.
Related Insight
Before you sign off on your bathroom build find out what the bathroom renovation laws in Victoria require for Melbourne homeowners.
Story Close: From Budget Shock to Smart Build
Many Melbourne homeowners start with the same surprise. What seemed like a small bathroom project quickly doubles in cost once permits, plumbing, and compliance come into view. Yet, with the right preparation, that shock turns into confidence.
Understanding the real numbers, working with registered trades, and budgeting realistically are the keys to a smooth build. Skilled Tradies Melbourne helps homeowners plan and execute bathroom extensions efficiently, even on occupied job sites.
With transparent quotes and reliable timelines, you can build your new bathroom or granny flat without the stress or the nasty surprises.
Sources: ArchiPro, Victorian Building Authority (VBA), CHOICE, Reddit (2025 data), SmarterBathrooms, RACV, and Skilled Tradies Melbourne project estimates.
